1. Field of the Invention
This invention relates to a constant velocity universal joint used in the power transmission systems of automobiles and various industrial machines and adapted for smooth transmission of torque regardless of whatever angles (operating angles) the rotary shafts on the driving and driven sides may take. Particularly, it relates to a constant velocity universal joint of the type which does not make an axial slide (plunging) or the so-called fixed type, and more particularly, it relates to improvements in the end shape of a track groove which opens to the larger end surface of an outer joint member.
2. Description of the Prior Art
As shown in FIGS. 6A, 6B and 8, a fixed type constant velocity universal joint 1 comprises an outer joint member 2 having tack grooves 24 formed in the spherical inner surface 22 thereof, an inner joint member 3 having track grooves 34 formed in the spherical outer surface 32 thereof, balls 4 incorporated between the respective pairs of track grooves 24 and 34 of the outer and inner joint members 2 and 3, and a cage 5 incorporated between the outer and inner joint members 2 and 3 and formed with pockets 56 for receiving the balls 4.
In the fixed type constant velocity universal joint 1, as shown in FIG. 9, the inner diameter D1 at the open end of the outer joint member 2 is smaller than the outer diameter D2 of the cage 5; therefore, it is necessary that after the inner joint member 3 and the cage 5 have been incorporated in the outer joint member 2, the inner joint member 3 and the cage 5 be inclined to expose one of the pockets 56 of the cage 5 to the outside through the open end of the outer joint member 2, and then a ball 4 be incorporated into the pocket 56. The incorporation of the inner joint member 3 and cage 5 in the outer joint member 2 is effected, as shown in FIG. 10, by inclining the inner joint member 3 and cage 5 through 90.degree., inserting the inner joint member 3 in the cage 5, relatively turning the two parts through 90.degree. in the direction in which the cage 5 and inner joint member 3 are coaxial with each other, and incorporating the inner joint member 3 in the cage 5. Then, as shown in FIG. 11, the cage-equipped inner joint member 3 and the outer joint member 2 are relatively inclined through 90.degree., the cage-equipped inner joint member 3 is inserted in the outer joint member 2, the two parts are inclined through 90.degree. in the direction in which the outer and inner joint members 2 and 3 are coaxial with each other, and the cage-equipped inner joint member 3 is incorporated in the outer joint member 2.
In the fixed type constant velocity universal joint 1, when torque is transmitted between the outer and inner joint members 2 and 3 at an operation angle .theta. (FIGS. 7 and 8), the balls 4 move circumferentially of the cage 5 within the pockets 56. The amount of movement of the balls 4 increases in proportion to the operating angle .theta.. The angle of inclination of the cage 5 with respect to the outer joint member 2 is at a maximum when the balls 4 are incorporated as shown in FIG. 9 (this angle being referred to as the ball incorporating angle), and it is necessary to determine the peripheral length of the pockets 56 on the basis of the amount of movement of the balls 4 obtained at this time. Therefore, there is a relation such that as the ball incorporating angle increases, the width (circumferential dimension) of a column portion 58 between adjacent pockets 56 decreases and so do the areas of the inner and outer spherical surfaces 52 and 54 of the cage 5.
When constant velocity universal joints used in automobiles and the like are applied, e.g., to the driving shaft of front-wheel-drive cars, a slide type constant velocity universal joint is disposed on the differential-associated side and a fixed type constant velocity universal joint is disposed on the wheel-associated side and these two joints are connected by a shaft. Since the fixed type constant velocity universal joint operates in association with the movement of the steering wheel and makes the same movement as that of the ground-engaging wheel, it is necessary for the fixed type constant velocity universal joint to operates at a high operating angle. Since the fixed type constant velocity universal joint rotates and transmits torque at a high operating angle in this manner, it is required to have sufficient rigidity, strength and durability. For this reason, the outer rig 2, inner joint member 3, balls 4, and cage 5 of the fixed type constant velocity universal joint 1 are hardened before use by a heat treatment, such as carburizing or induction hardening. Usually, the component in the fixed type constant velocity universal joint 1 which is most vulnerable in an operation at a high operating angle is the cage 5. As the operating angle .theta. increases, the proportion of the portion of the cage 5 that overhangs the spherical inner surface 22 of the outer joint member 2 and the spherical outer surface 32 of the inner joint member 3 increases (FIGS. 7 and 8) and so does the axial force ion the balls 4. Therefore, the strength of the cage 5 sharply decreases when the operating angle takes a high value.
Further, in recent years, there has been a desire to improve milage of vehicles, the most prospective means to meet the desire being to reduce the weight of the vehicle, and it is also strongly desired to provide a light-weight compact version of the constant velocity universal joint. In making the fixed type constant velocity universal joint 1 lightweight and compact, it is essential to increase the strength of the cage 5, a component which is most vulnerable in an operation at a high operating angle, to the greatest extent. As measures therefor, it has been proposed to strengthen the material as by heat treatment. At any rate, however, there is a problem of cost increase. Increasing the thickness of the cage 5 would increase the strength; on the other hand, however, it is irrational in that it decreases the depths of the track grooves of the inner and outer joint members 3 and 2, which decrease, in turn, leads to a lowering of the allowable load torque and a considerable lowering of the durability. Further, the region of the cage 5 which is liable to break is the column portion 58 between adjacent pockets 56 which receive balls 4. Therefore, if the width of the column portion 58 is increased, the strength will increase. To this end, one may contemplate decreasing the ball diameter or increasing the PCD of the balls; however, both of the measures are undesirable in that the former lowers the durability of the joint and the latter increases the outer diameter of the joint.
FIG. 12A and FIG. 12B show the inlet portion of the track groove 24 of the outer joint member 2 in a conventional fixed type constant velocity universal joint 1. The inlet portion of the track groove 24 is cut by a conical surface 27 determined by a shaft 36 when the latter takes a maximum operating angle .theta. (see FIGS. 7 and 8), and the position of the open end surface 26 is outside the conical surface 27 including the sectional plane of the cut end of the track groove. However, when compact formation is to be attained as by decreasing the PCD of balls 4, it is necessary, particularly where the number of balls is large (seven or more balls), to set the ball incorporating angle .alpha. for incorporating balls 4 at a smaller value than in the prior art because of the need to secure the width of the column portion 58 of the cage 5. However, if the ball incorporating angle .alpha. is decreased (.alpha..sub.1 &gt;.alpha..sub.2), as shown in FIG. 13A and FIG. 13B, it becomes necessary to set the open end surface 26 at an intermediate position on the sectional plane of the cut end of the track groove of the conical surface 27. That is, the open end surface 26 of the outer joint member 2 is moved more backward than in the prior art (A.sub.1 &gt;A.sub.2). This means that the arrangement having such outer joint member shape aiming at compact formation, as compared with the conventional arrangement, results in a lowering of the outer joint member strength associated with a high operating angle.